Limited expansion rock bolt anchor



l pril 23, 1968 c. WILLIAMS LIMITED EXPANSION ROCK BOLT ANCHOR FiledApril 4, 196e United States Patent O 3,379,089 LIlVIITED EXPANSION ROCKBOLT ANCHOR Chester I. Williams, 347 Greenbriar SE., Grand Rapids, Mich.49506 Filed Apr. 4, 1966, Ser. No. 539,857 2 Claims. (Cl. 85-73)ABSTRACT OF THE DISCLOSURE A rock anchor with a cone expander surroundedby an expansible shell, in which relative axial movement be- -tween theexpander and the shell is limited by interengageable abutments on theexpander and shell.

This invention relates to the construction of anchoring devices forsecuring the inner end of a bolt in a hole in rock or concrete. One typeof bolt anchor in current use is based upon Athe action of a cone-shapednut in threaded engagement with the bolt rod. Rotation of the bolt pullsthe cone nut toward the entrance of the hole in the rock, and into anexpansible shell surrounding the nut. This wedging action jams the shelloutward against the wall of the hole, and produces the anchoring action.Once the anchor has been set in this manner, the load on the bolt rod istransmitted through the inclined cone surface to continue the radialpressure.

A problem has been encountered in cases where -the rock formation issoft or resilient, or when the bolt is installed in concrete not yetfully cured. In a material such as this, the shell can be forced farenough into the rock-even in a hole initially just large enough toreceive the anchor-to permit the expander cone to pull completelythrough the shell. The present invention provides an improvement in thistype of anchor that prevents this pull-out. In summary, interengageableabutments are provided on the cone and shell that limit the relativesliding of the cone and shell to a Ipredetermined amount. Forces arethereafter transmitted from the cone to the shell in an axial directionwithout further increase in the pressure on the inclined surfaces.Several modifications of the present invention are presented to providefeatures desirable in particular installations. The several features ofthe invention will be analyzed in detail through a discussion of theparticular embodiments illustrated in the accompanying drawing.

In the drawing:

FIGURE l is a sectional elevation showing the installation of a bolt ina hole in concrete or a rock formation, with lthe anchoring device shownpartially in section in the condition as initially installed.

FIGURE 2 is a sectional elevation similar to FIGURE 1, but showing theanchor device in the fully-exposed condition.

FIGURE 3 is a perspective view on a somewhat enlarged scale of theexpansible shell and thrust abutment assembly shown in FIGURES l and 2.

FIGURE 4 is a perspective View of the cone-shaped expanding nut of theassembly illustrated in FIGURES 1 and 2.

FIGURE 5 is an elevation, partially in section, of a modified form ofthe invention, in the unexpanded condition.

FIGURE 6 is a view of the mechanism shown in FIG- URE 5, inthe fullyexpanded condition.

FIGURE 7 is a sectional elevation showing a modified form of coneconstruction.

FIGURE 8 is a sectional elevation of a further modication of theinvention, in the unexpanded condition.

FIGURE 9 is a section on the plane 9-9 of FIG- URE 8.

Patented Apr. 23, 1968 FIGURE 10 is a section on the plane 10-10 of FIG-URE 8.

Referring to FIGURES 1 and 2, the rock bolt generally indicated at 10 isshown installed in the hole 11 in the rock formation 12. The outer end13 of the bolt is threaded to receive a nu-t, and a relatively heavybearing plate is usually interposed between the nut and the surface 14of the rock formation. The nut and the bearing plate are conventional,and are not shown in the drawings.

A cone-shaped nut 15 is in threaded engagement with the inner end 16 ofthe bolt rod, and clockwise rotation of the rod from the surface willproduce an axial movement of the nut 15 to the left, as shown in FIGURESl and 2. The expansible shell 17 surrounds a portion of the nut, and iswedged to an increased ci-rcumscribed diameter as the nut begins itsaxial movement. The axial thrust on the shell 17 produced by themovement of the cone nut is resisted by the abutment ring 18 and thetrusttransfer washers 19, since relative rotation will normally takeplace between the thrust ring 18 and the left end of the Shell 17. Theabutment -ring 18 is normally in threaded engagement with the end 16 ofthe rod, and its axial placement ywith respect to the rod is assured bythe provision of the flattened area 20 which supplements the end of thethreading on the rod to prevent further axial movement of the ring 18 asthe thrust forces from the nut 15 increase.

To assure that the relative axial movement between the cone 15 and theshell 17 is limited to the position shown in FIGURE 2, an annularshoulder 21 is provided on the inside surface of the shell 17 which isengageable with the left end 22 of the cone when these two membersarrive at the FIGURE 2 position. The forces generated at the annularshoulder are in a primarily axial direction, and supplement the axialcomponent of the jamming action generated on the inclined peripheralsurface of the cone 15 acting against the similarly-shaped conicalinside surface of the shell 17. Because of the well-known stickslipcharacteristics of friction, it is most likely Ithat the shoulder 21will not have to sustain a shear stress as large as might appear to bethe case. Once the relative sliding movement between the cone and theshell has been completely halted by the presence of the shoulder, thefriction characteristics of a completely static nature will developbetween the peripheral surface of ythe cone 15 and the inside surface ofthe shell 17 `to develop further resistance to pull-out.

The initial rotative restraint which permits rotation of the rod fromthe surface to induce movement of the nut 15 is caused by the drag ofthe nut and the shell 17 against the wall of the hole 11. To assure thatthe shell and nut are rotatively fixed with respect to each other, andto further increase the drag against the wall of the rock formation, theridge 23 is provided on the periphery of the cone 1S. This ridge isreceived within the peripheral discontinuity 24 of the expansible shell17, with this configuration resulting in a generally C-shapedconfiguration for the shell. This particular feature is well-known, andforms no part of the present invention.

Referring to FIGURE 5, the bolt 25 may be similar in all respects to thebolt 10 shown in FIGURE l. The abutment ring 26 and the thrust-transferwashers 27 are also similar, but the shell 28 has a continuous conicalinterior surface, without the provision of the shoulder 21. In theFIGURE 5 modification, the expansion induced by the cone nut 29 islimited by the engagement of the shoulder 30 on the nut with the end 31of the shell 28. The ridge 32 is preferably included on lthis form ofnut also, and is received in a discontinuity in the side of the shell 28as previously described. One advantage of the placement of the abutmenton the large end of the cone, rather than on the relatively small leftend of the interior surface of the shell, is that the increasedperipheral distance correspondingly increases the potential shearresistance of the material forming the shoulder on the cone over that ofthe available peripheral length of the material forming the shoulder 21on the shell. It is also usual practice to form the cone 29 of asomewhat stronger material than that of the shell 28, so the provisionof the shoulder on the stronger material is also an advantage. It shouldbe noted that both the arrangements shown in FIGURES 1-2 and that shownin FIGURES 5-6 require a slightly greater diameter in the hole for agiven degree of clearance and expansion, assuming the same slope on theperipheral surface of the cone and interior of the shell.

The modification shown in FIGURE 7 illustrates the manner which the samegeneral effect as that provided by the shoulder 30 can result from atwo-piece cone construction. The cone 33 has a tapered body portion 34,and a ring 35 in threaded engagement with the large end ofthe cone. Itis preferable that the hand of the threaded engagement of the ring withthe body 34 be of opposite hand to that of the thread system 36 on theinterior of the cone, and which engages the threaded inner end of thebolt rod. This arrangement eliminates the possibility that the rotationof the rod during the setting of the anchor might accidentallyback-rotate the ring 35, and loosen it to the point where it cannotperform its function.

The modification shown in FIGURE S, supplemented by FIGURES 9 and 10,illustrates an arrangement for limiting the penetration of the cone nut37 into the shell 38 without substantial increase in the circumscribedinitial diameter required for a given degree of expansion. The C-shapedshell 38 has the usual discontinuity shown at 39 in FIGURE 10, and alsohas a recess 40 on the interior surface at the diametrically oppositeside. This recess receives the relatively wide projection 41 on thesurface of the cone nut 37, and a point is ultimately reached in whichthe end 42 of this projection collides with the shoulder 43 that definesthe left axial end of the recess 40. The expansion of the shell 38 asthe bolt rod 44 is rotated with respect to the nut 37 produces axialforces that are resisted by the abutment ring 45 as previouslydescribed, and this expansion produces a clam shell-type opening of theshell 38. The presence of the recess 40 produces a desirable point ofweakness at a predetermined position, and the shell will rupture alongan axial plane that intersects this recess. Since it is desirable toassure that both sides of the shell 38 (on the opposite sides of therupture plane) are still engaged by the shoulder 42, it is preferable toprovide a notch in the position shown at 46 in a generally axialdirection along the central area of the portion of the shell 38 -thatdefines the shoulder 43. This will tend to assure that the crack willtake place in the middle of the shoulder, and thus leave some portionsof the shoulder 43 -on both sides of the crack for engagement with theend 42 of the projection 41.

The particular embodiments of the present invention which have beenillustrated and discussed herein are for illustrative purposes only andare not to be considered as a limitation upon the scope of the appendedclaims. In these claims, it is my intent to claim the entire inventiondisclosed herein, except as I am limited by the prior art.

I claim:

1. In a rock anchor including a threaded rod section,

a generally cone-shaped expander having a major and a minor end, and inthreaded engagement with said rod section, a ring normally axially fixedwith respect to said rod section, and disposed opposite and initiallyspaced from the minor end of said expander, and an expansible shellhaving an interior surface normally bearing on the peripheral surface ofsaid expander, and having an end normally engaging said ring, theimprovement comprising:

means on said shell defining an axial discontinuity along one sidethereof providing a C-shaped configuration in cross section, said shellhaving and axially-extending recess in 4the interior surface thereofdiametrically opposite from said discontinuity and terminating at apoint spaced from the end of said shell adjacent to said ring, saidexpander having a peripheral projection received in said recess, theends of said projection and recess forming abutments limiting relativeaxial movement between said shell and said expander, said shell alsohaving an axial groove on the interior surface thereof in alignment withthe center of said recess to provide a point of stress concentration andlocalize fracture of said shell so that both of the separating sidesthereof will be engaged by the end of said projection. 2. In a rockanchor including a threaded rod section, a generally cone-shapedexpander having a major and a minor end, and in threaded engagement withsaid rod section, a ring normally axially fixed with respect to said rodsection, and disposed opposite and initially spaced from the minor endof said expander, an an expansible shell having an interior surfacenormally bearing on the peripheral surface of said expander, and havingan end normally engaging said ring, the improvement comprising:

means forming a ring portion on said expander, said ring portion beingin threaded engagement with said expander with threading of oppositehand to that of said rod section, said ring portion forming a shoulderadjacent the major end of said expander, and initially spaced from thevadjacent end of said shell and engageable therewith yto limit relativesliding movement between said shell interior surface and said expanderperipheral surface after substantial relative movement along saidsurfaces has taken place to induce limited expansion of said shellfollowed by direct axial transfer of forces between said expander andsaid shell.

References Cited UNITED STATES PATENTS 674,715 5/ 1901 Summerer 85-751,120,368 12/1914 Booraem et al 85-75 1,469,665 10/ 1923 Pleister et al.85-76 1,549,326 8/1925 Pleister 85-76 1,959,439 5/1934 McIntosh 85-753,227,031 1/ 1966 Williams 85-75 3,152,375 10/1964 Blakeley 85-77FOREIGN PATENTS 223,908 6/1957 Australia.

EDWARD C. ALLEN, Primary Examiner.

